CONFIG_X86_X2APIC: x2APIC interrupt controller architecture support

General informations

The Linux kernel configuration item CONFIG_X86_X2APIC has multiple definitions:

x2APIC interrupt controller architecture support found in arch/x86/Kconfig

The configuration item CONFIG_X86_X2APIC:

• prompt: x2APIC interrupt controller architecture support
• type: bool
• depends on: CONFIG_X86_LOCAL_APIC && CONFIG_X86_64 && ( CONFIG_IRQ_REMAP || CONFIG_HYPERVISOR_GUEST )
• defined in arch/x86/Kconfig
• found in Linux kernels: 6.15, 6.16-rc+HEAD

Help text

x2APIC is an interrupt controller architecture, a component of which (the local APIC) is present in the CPU. It allows faster access to the local APIC and supports a larger number of CPUs in the system than the predecessors.

x2APIC was introduced in Intel CPUs around 2008 and in AMD EPYC CPUs in 2019, but it can be disabled by the BIOS. It is also frequently emulated in virtual machines, even when the host CPU does not support it. Support in the CPU can be checked by executing grep x2apic /proc/cpuinfo

If this configuration option is disabled, the kernel will boot with very reduced functionality and performance on some platforms that have x2APIC enabled. On the other hand, on hardware that does not support x2APIC, a kernel with this option enabled will just fallback to older APIC implementations.

If in doubt, say Y.

Support x2apic found in arch/x86/Kconfig

The configuration item CONFIG_X86_X2APIC:

• prompt: Support x2apic
• type: bool
• depends on: CONFIG_X86_LOCAL_APIC && CONFIG_X86_64 && ( CONFIG_IRQ_REMAP || CONFIG_HYPERVISOR_GUEST )
• defined in arch/x86/Kconfig
• found in Linux kernels: 2.6.30–2.6.39, 3.0–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.14

Help text

This enables x2apic support on CPUs that have this feature.

This allows 32-bit apic IDs (so it can support very large systems), and accesses the local apic via MSRs not via mmio.

Some Intel systems circa 2022 and later are locked into x2APIC mode and can not fall back to the legacy APIC modes if SGX or TDX are enabled in the BIOS. They will boot with very reduced functionality without enabling this option.

If you don't know what to do here, say N.

Hardware

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The data is retrived from:

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